Energy can neither be created nor destroyed. However, it can be changed from one form to another. This important idea is called the Law of Conservation of Energy.

BACKGROUND

When water trapped behind a dam is channeled to push on the blades of a turbine, the potential energy of the still water changes form. When the water starts to move, the potential energy becomes kinetic energy. When the turbine starts to spin, the kinetic energy becomes a specific kind of kinetic energy called mechanical energy
The spinning motion of the turbine is used to rotate a coil of copper wire between two opposite magnetic poles. This starts electrons moving down the wire. When the coil of copper wire rotates past the North magnetic pole, the electrons move down the wire in one direction. When the coil rotates past the South magnetic pole, the electrons reverse direction. This back-and-forth flow of electricity through a wire is called alternating current-otherwise known as AC. A device in which coils of copper wire are rotated through magnetic fields to generate electric current is called a dynamo.

LESSON OBJECTIVES

Students will:

Discuss magnets and magnetism in class.

Discuss the idea of changing one kind or form of energy into another.

Draw a diagram of a simple generator; a coil of copper wire rotating in a magnetic field.

Physical Science, Transfer of Energy: Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei, and the nature of a chemical. Energy is transferred in many ways.

First, use the wire to make a coil of about 40 turns and about 3 or 4 inches in diameter. Next, wrap about 25 turns of the wire around a compass. Connect the two coils together at both ends to make a complete circuit. Pass the magnet back and forth through the center of the first coil. Watch the compass needle.

What happens when you move the magnet in one direction? In the other direction? (The needle is deflected, first in one direction, then in the other.) Why does this happen? (As the magnet moves through the coil, electrons move in the coil. This is an electric current, of course. When this current is passed to the winding around the compass, it causes a magnetic field to surround the compass winding. This magnetic field causes the compass needle to move, just in the same way that Earth's magnetic field causes a compass needle to move.)

For more fun, you could connect the two ends of the first coil to a microampere meter that measures electrical current and repeat the experiment. What happens to the meter's needle? (As one pole of the magnet moves through the winding, the needle moves in one direction. When the other pole of the magnet passes through the winding, the needle moves in the opposite direction.) Why? (The purpose of the microampere meter, which measures very, very small amounts of current, is to indicate a flow of current in one direction or the other. This kind of meter is a more sophisticated version of a compass wound with magnet wire.)

Explore the World Outside

Ask students to list places where an electrical generator might be needed during a power failure, or places where they have seen portable generators in use. (Emergency generators are used in homes, hospitals, and apartment houses; portable generators are used to run farm equipment and amusement park rides, etc.)

Explore the Film and Web Site

Present related clips from the film Tesla: Master of Lightning to the class. The following are some suggestions:

04:30 - 11:41
My Early Years: Tesla's early education

11:41 - 18:36
New Land: Tesla's arrival in America

23:21 - 27:40
Niagara: Overview of the first hydroelectric plant

After viewing select clips from the film, direct students through the interactive tour of Tesla's Niagara power
system on this site. Ask students to locate the stage at which the kinetic energy inherent in flowing water is changed into mechanical energy. (When the flowing water hits the turbines.) Ask students to locate the dynamo in the Niagara power plant.

What Do You Think?

Ask students to create a diagram showing the transformations of energy that occur when water trapped behind a dam is used to generate electricity.

ASSESSMENT RECOMMENDATIONS

The teacher should consider the following when assessing students:

Participation in class discussion.

How well were the students able to make the experiment work.

How well could the students explain the experiment and how it relates to a large generator.

How well students could relate to changing one type of energy to another.

EXTENSIONS

Guide students through a discussion of what happens inside an electrical generator or dynamo. A coil of many turns of copper wire is rotated between the North and South poles of a very powerful magnet. As the rotating coil of wire passes one pole of the magnet, electrons in the wire are pushed in one direction. When the rotating coil of wire passes the other pole of the magnet, these electrons are pulled in the opposite direction. Because the electrical current keeps reversing direction, it is called alternating current.